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The Spiral model is a system development lifecycle model used in information technology. This model combines the features of the prototyping model and the waterfall model. It is a software project that repeatedly passes through phases in iterations called spirals.
It follows four steps in its process they are:
1. PLanning: In this phase they identify the objectives, identify the alternative means of implementing this portion of the product and identify the constraints of the alternatives.
2. Risk Analysis: Here they evalaute the alternatives relative to constraints and objectives.They also evaluate the risk involves with each alternative and finally conduct a risk resoultion.
3.Engineering: Here they must develop and verify the product.
4.Evalauation: Then they mustv plan the next phase. Depending on the next phase it could be a requirements plan, an integration plan.
The Spiral model is mainly used in large projects and medium to high risk projects. It is also used when users are unsure of their needs and requirements are complex.
There are many strengths and weaknesses with the Spiral model. Some of the main strengths are:
Estimates such as budget get more realastic as work progresses as important issues are discovered earlier.
It is also more able to cope with the changes that software development generally entails.
Software engineers can get their hands in and start working on a project earlier.
There are also disadvantages to the Spiral model they are:
The time that is spent evluating risk is too large for small or low risk models.
The time that is spent planning, resetting objectives, doing risk analysis and prototyping may be excessive.
It is also a complex model.
It also may be hard to define the objective.
The spiral could also continue indefinitely.